P R E D IC T IO N O F C A R B O N -13 C H E M IC A L S H IF T V A L U E S A N D 2D N M R S T U D IE S O F A C R Y L O N IT R IL E C O P O L Y M E R S
by
J A S P R E E T K A U R
D ep artm en t o f ch em istry
su b m itted
in fu lfillm e n t o f th e re q u irem en ts o f the d eg ree o f D o c to r o f P h ilo so p h y
to th e
In d ia n In stitu te o f T ech n o lo g y , D elh i M a y , 2 0 0 7
: 678- 7W.3Z
~7ftS - P
I. I. T. DELHI.
I ik/us* MaT^U
Dedicated to my parents
Certificate
This is to certify that the thesis entitled “Prediction o f carbon-13 chemical shift values and 2D N M R studies o f acrylonitrile copolymers” being submitted by Jaspreet Kaur to the Indian Institute o f Technology, Delhi for the award o f Doctor of Philosophy is
a record o f bonafide research work carried out by her. Jaspreet K aur has worked under my guidance and supervision and has fulfilled the requirements for the submission o f thesis which to my knowledge has reached the requisite standards.
The results contained in this thesis have not been submitted in part or full to any other university or institute for the award o f any degree / diploma.
Professor,
Department o f Chemistry,
Indian Institute o f Technology, Delhi, Hauz Khas, N ew Delhi 110016.
Acknowledgements
This work has been a journey o f growth and development bundled with many challenges, failures and few rewarding experiences. During this, I have learned numerous new indispensable pieces o f knowledge o f contemporary science. All this has been a memorable experience for which I am grateful.
I would like to convey my supreme gratitude to my supervisor, Prof. A.S. Brar for presenting me the opportunity to work under his guidance. This thesis grew out of a series o f dialogues with my supervisor Professor. His comments on papers and chapter drafts are in themselves a course in critical thought upon which I will always draw.
I am obliged to present and ex- Head o f Department, Prof. B. Jayaram, Prof. U. K.
N adir for extending the funds and facilities essential for carrying out this research work.
I desire to take this opportunity to thank esteemed teachers, Dr. N. D. Kurur for teaching me N M R and Dr. Jayadeva o f electrical engineering department for teaching and clearing m y doubts related to neural networks.
Support o f technicians especially Mr. Munnalal and non-teaching staff is really appreciated.
I can not articulate my feelings for my husband, Dr. Mukesh who with all the patience, understanding and love stayed with me in all the weathers. I w ant to thank him for making my life simple, easy and enjoyable; for making me more confident and for helping m e in adjusting with his loving family.
I am forever grateful to my parents, whose foresight and values paved the way for the privileged education and for gently offering counsel and unconditional support at
each turn o f the road. I heartfully thank my sis Sandy for supporting me w hen ever I feel low and m y bro Guki for his funny ways o f making my life cool.
I w ish to appreciate all o f my batch mates and friends. I relished the company o f all m y labmates and juniors particularly o f Gurmeet, Sukhi, Meghna, Tripta, Sonia, Pravin, Puneeta and Ashok. I w ish to thank Sonia for all the support, company and entertainment she has provided during the last stages o f my thesis.
In the last but not the least I want to thank almighty for showing m e the right path.
Jaspreet K aur
Abstract
Copolymerization is the most eminent and powerful method for effecting systematic changes in polym er properties. It generally incorporates two or more different monom er bearing diverse physical and/or chemical properties and lead to the formation o f new materials with immense scientific and commercial importance. It modulates both intra- and intermolecular forces exercised between like and unlike segments and hence the properties such as glass transition temperature, solubility, dyeability, adhesion, elasticity, crystallinity and chemical reactivity w hich may be varied within wide limits.
One o f the simplest procedures for accomplishing copolymerization is free radical polymerization and it has two significant advantages first, it doesn't require rigorous experimental conditions and second it can be implemented to large variety o f monomers.
Elucidation o f copolymer structure (copolymer composition, monom er sequence distribution) is of foremost concern for the prediction o f copolymer properties in addition to correlation between structure and properties. One o f the main established functions o f NM R in polymer science is the structural characterization o f the copolymers, which provides the link between structure-property relationships. One dimensional NM R
1 1 1
techniques ( H, C{ H}, DEPT etc.) in conjugation with two-dimensional techniques such as HSQC, TOCSY and HMBC provides a competent means for the stereochemical investigation o f polymers. HSQC and HMBC techniques provide correlations between the resonances o f 'H and 13C nuclei having one-(HSQC), two- or three-(HMBC) bond couplings. TOCSY in conjugation with HSQC provides one to one correlation between protons giving information about various vicinal and geminal couplings.
Chapter 1
This chapter submits the literature survey about the role o f modern NM R spectroscopic techniques hitherto in the solution o f complex structural elucidation problems o f the contemporary polymer research. Here, we also presents the brief overview o f the theoretical approaches utilized in prediction o f carbon-13 N M R chemical shifts and hence the microstructure o f copolymers.
Chapter 2
This chapter describes various computational (Back propagation algorithm used to predict the carbon-13 chemical shift values) and experimental protocols along with details o f the conditions followed in homo and copolymerization o f acrylonitrile monomer w ith methyl acrylate, ethyl acrylate, butyl methacrylate, 2-hydroxy ethyl methacrylate and 2-vinyl pyridine besides giving a brief account o f various experimental techniques utilized throughout the current research work
The experimental details for recording o f ID ('H , ^ C l'H } , DEPT-135, 90, quantitative carbon-13) N M R and 2D (heteronuclear single quantum correlation (HSQC), total correlation spectroscopy (TOCSY) and heteronuclear multiple bond correlation (HMBC)) N M R experiments are also incorporated. Furthermore, the details o f the calculation o f outfeed compositions and reactivity ratios are added.
Chapter 3
13 •
C N M R spectral simulation techniques can provide assistance in the solution o f complex structural elucidation problems. These are based on the existence o f direct yet
complex relationship between the observed chemical shifts o f carbon atom and its environment.
Herein, we have utilized artificial neural network (three layered neural network) for the to simulate the ^ C l'H } N M R chemical shifts for the hydrogen terminated fragments o f acrylonitrile copolymers and comparison was done with carbon-13 chemical shift values predicted by partial least square regression analysis (PLSR).
Here, to link molecular structure with the chemical shift values, an indirect approach was applied. This approach was realized in two steps:
(a) Representing each copolym er’s molecular structure with numerical descriptors, which adequately describes the chemical environment.
(b) Choosing only those subsets o f the descriptors which are information rich and building good models that can predict chemical shift value.
The generated models were cross-validated using leave-n-out method (n = l) o f cross-validation. Each model was validated 50 times in order to obtain reliable statistics and establish the true generalization capabilities o f resulting model. Neural Network gave mean absolute error (mae) =1.4 ppm (partial least square regression gave mae = 5.0 ppm) indicating that neural network can be used to predict carbon-13 N M R chemical shift information and hence micro structure o f the copolymers.
Subsequently, the 13C chemical shift values o f methine and methylene carbon atoms o f acrylonitrile/butyl methacrylate and acrylonitrile/ethyl acrylate copolymers were predicted w ith the average m ean absolute error o f various carbons varies between 0.4 to
1.3 ppm. The calculated chemical shift values have good correlation with the experimental values. The results were compared w ith partial least square regression method, which gave the error between 2.0-5.5 ppm.
Chapter 4
The copolymers o f alkyl acrylate find their uses as binders, coating and paints etc.
The incorporation o f methyl acrylate to a suitable level in the copolymers o f acrylonitrile reduces its melting temperature thus improving its processability. This chapter offers the studies carried out regarding the microstructure elucidation o f Acrylonitrile/M ethyl acrylate (A/M) and Acrylonitrile/Ethyl acrylate (A/E) copolymers. The A/M and A/E copolymers having different monomer compositions were synthesized using solution polymerization and the composition o f resultant A/M copolymers was determined using quantitative 13C {lH} NMR. The values o f reactivity ratios in case o f A/M copolymer indicate that there is random placement o f two monomers along the copolymer chain. The methine and methylene regions in n C {1H} N M R spectrum o f acrylonitrile-m ethyl acrylate copolymer were distinguished with the help o f D EPT-135. Correlations between carbon and proton signals were obtained from the lH - 13C heteronuclear single quantum correlation (HSQC) o f A/M copolymer. M ethine carbons o f A and M unit shows compositional as well as configurational sensitivity upto triad level. In order to establish various connectivities in the copolymer chain, the TOCSY spectra were recorded. Two and three bond coupling between protons o f different groups that are directly coupled in A/M copolymer was seen in TOCSY experiment. Heteronuclear multiple-bond correlation spectroscopy has been used to study carbon (carbonyl/nitrile)-proton
coupling. The carbonyl and nitrile carbons showed compositional sensitivity upto the triad level.
Acrylonitrile/Ethyl acrylate copolymers revealed similar trend in ID and 2D NM R as exhibited by acrylonitrile and methyl acrylate copolymers.
Chapter 5
Synthetic polymers derived from functional methacrylates have been widely used in industry, agriculture and medicine owing to their remarkable properties such as potential biocompatibility. This chapter provides the detail description o f the microstructure elucidation through sequentially assigned ID and 2D N M R spectra o f various acrylonitrile-(butyl and 2-hydroxy ethyl) methacrylate copolymers along with their composition and the reactivity ratios o f monomers in these copolymers.
The copolymer compositions o f acrylonitrile/butyl methacrylate (A/B) and acrylonitrile/2-hydroxy ethyl methacrylate (A/H) copolymers were ascertained from
13 1
quantitative C{ H} N M R spectra by quantifying carbonyl and nitrile carbons. The values o f reactivity ratio affirm that methacrylate monomers are more reactive than acrylonitirile monomer towards propagating chain.
The quaternary and methylene carbon-13 signals were found to be broad and overlapped. Hence, differentiated and recognized with the help o f DEPT-135. Especial emphasis was given to the resonances o f methine, a-methyl and methylene carbon which were rich in information about microstructure o f copolymer. In HSQC studies, it was seen that the methine carbon/proton resonances showed both stereochemical and compositional sensitivity. By comparing the HSQC spectrum o f polyacrylonirile with
viii
those of copolymers (A/B) o f various compositions, it was noticed that the methine region was further splitted and A centered unit was assigned to AAA, AAB and BAB triads respectively. The spectral region attributed to AAA triad decreased in intensity as acrylonitrile content in the copolymer reduced. This triad region also exhibited configurational sensitivity and were assigned to ArArA, ArAmA and AmAmA triads respectively. The AAB triad showed further compositional sensitivity and was assigned to AAABA, AAABB and BAABB pentads. Out o f which AAABA and AAABB were observed to be configurationally sensitive. These assignments were verified with the help o f TOCSY. Similarly, by comparing the HSQC spectra of A/B copolymer o f different compositions, BAB triad was assigned up to pentad level (ABABA, ABABB and BBABB). ABABA and ABABB pentad showed configurational sensitivity. The configurations in various pentads were affirmed via TOCSY. Methylene and a-methyl regions were similarly assigned with the help o f HSQC upto triad, tetrad and pentad levels. In order to comprehend the connectivity and to ascertain various couplings in the copolymer chain, TOCSY spectra were recorded and assignments were done. Two and three bond coupling between protons o f different groups that are directly coupled in A/B copolymer can be seen in TOCSY experiment at low mixing time. The methine protons in various triads and pentads exhibited three-bond coupling with the methylene protons o f various dyads and tetrads.
Heteronuclear multiple-bond correlation (HMBC) has been employed to study carbon (carbonyl/nitrile)-proton coupling. The carbonyl and nitrile carbons expressed compositional sensitivity up to the triad level. HMBC reasserted the assignments done with 2D-HSQC and TOCSY experiments
Acrylonitrile/2-Hydroxy ethyl methacrylate: These acrylonitrile-methacrylate copolymers showed compositional sensitivity up to triad and tetrad level with meso and racemic configurations for methine, methylene and a-m ethyl resonances. Various 2D (HSQC, TOCSY, and HMBC) N M R techniques in conjugation w ith ID (1H, ^ C l'H } , and DEPT) N M R experiments have been exploited as an efficacious method for analysis o f the microstructure o f acrylonitrile-2-hydroxy ethyl methacrylate copolymers.
Chapter 6
Homo- and copolymers o f 2-vinylpyridine has numerous remarkable applications such as stabilizers, catalysts, extractants, conductors etc. This chapter is based on the copolymers o f 2-vinyl pyridine w ith acrylonitrile. The Acrylonitrile/2-vinylpyridine (A/V) copolymers were synthesized using bulk polymerization route. The values o f reactivity ratio were obtained again using copolymer composition data by Kelen-Tudos and non linear error in variable methods. The assignments o f carbon resonances were done with the help o f 13C{!H} N M R and DEPT-135 spectra o f A/V copolymer.
Particular interest was given to the resonance o f methine and methylene carbon signals which were rich in information about monomer unit sequence. Explicit information about compositional and configurational sequences was afforded by 2D HSQC in conjugation w ith TOCSY. Methine and methylene region depicted sensitivity towards both composition and configuration. HSQC showed compositional and configurational sensitivity o f A, P centered unit o f methine region up to the triad level while methylene region showed sensitivity to the dyad level.
TOCSY demonstrated two and three bond couplings between the protons o f different directly coupled groups. HMBC experiment exhibited nitrile carbon couplings
x
with the methine and methylene protons, HMBC in conjugation with HSQC and TOCSY strongly reaffirm ed the assignments. Thus, methine and methylene regions were comprehensively analyzed by 2D-NM R (HSQC, TOCSY and HMBC) spectroscopy which appropriated nJ (n = l(HSQC), 2 and 3 (TOCSY and HMBC)) bond couplings detection.
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Table of Contents
Page No
Certificate 1
Acknowledgem ents 11
Abstract *v
Chapter 1- Introduction
1.1 Introduction j
1.2 Free-Radical Polymerization and Characterization 4
1.3 NM R o f Polymers 5
1.3.1 NM R o f homo- and copolymers 7
1.4 M icrostructure o f polymers 1 2
1.5 Determ ination o f reactivity ratios 13
1.6 Prediction o f carbon-13 chemical shift values 14
References 22
Chapter 2- Experimental
2.1. Polym er synthesis 33
2.1.1 Purification o f reagents 33
2.1.2 Homopolymerization 33
2.1.3 Copolym erization 33
2.1 M olecular W eight Distribution 34
2.2 Copolym er Composition and Reactivity Ratio determination 34
2.3 NM R Studies 35
2.4.1 ID NM R measurements 35
2.4.2 2D NM R measurements 35
2.5 Back-Propagation Training Algorithm 36
References 37
Chapter 3- Prediction of carbon-13 chemical shift values
3.1 Introduction ^ 8
3.2 M ethodology 40
3.2.1 Approach to predict the 13C chemical shift values 40 3.2.2 Various steps followed in this approach 40
3.2.3 Copolym er Data Set 46
3.3 Results and Discussion 46
3.4 Conclusions ^ ^
R eferences 53
57
Chapter 4- Acrylonitrile/Methyl acrylate Acrylonitrile/Ethyl acrylate
4.1 Introduction
4.2 Acrylonitrile/Methyl acrylate copolymers ^ 9
4.2.1 Reactivity Ratio 5 9
4.2.2 13C{1H} NM R studies 6 0
4.2.3 HSQC NM R studies 61
4.2.4 *H NM R studies ^
4.2.5 2D-TOCSY studies
4.2.6 HMBC 63
4.3 Acrylonitrile/Ethyl acrylate copolymers 687 2
4.3.1 Reactivity Ratio
4.3.2 13C{1H} NM R studies ? 2
4.3.3 HSQC NM R studies ? 3
4.3.4 *H NM R studies 7^
4.3.5 2D TOCSY studies
4.3.6 HMBC ? 8
4.4 Conclusions gj
References ^
Chapter 5- Acrylonitrile/Butyl methacrylate
Acrylonitrile/2-hydroxy ethyl methacrylate
5.1 Introduction gg
5.2 Acrylonitrile/Butyl methacrylate copolymers 3 7
5.2.1 Reactivity ratio 3 7
5.2.2 ^C ^H } NM R studies 8 8
5.2.3 HSQC studies g9
5.2.3.1 Methine region 3 9
5.2.3.2 p-methylene region 9 2
5.2.3.3 a-m ethyl region 9 6
5.2.4 *H NM R studies 9 7
5.2.5 2D-TOCSY studies 98
5.2.6 HMBC 1 0 0
5.3 Aerylonitrile/2-hydroxy ethyl methacrylate copolymers 1 0 4
5.3.1 Reactivity ratio 1 0 4
5.3.2 13C{1H} NM R studies 1 0 5
5.3.2 HSQC Studies 106
5.3.3 !H and TOCSY studies HO
5.3.4 HMBC 1 1 2
5.4 Conclusions H3
R eferences 115
Chapter 6- Acrylonitrile/2-vinyl pyridine
6.1 Introduction 119
6.2 Acrylonitrile/2-vinyl pyridine 120
6.2.1 Reactivity ratio 120
6.2.2 “ C ^H } NM R studies 121
6.2.3 HSQC studies 122
6.2.3.1 Analysis of methylene region 122
6.2.3.2 Analysis o f methine region 123
6.2.4 1H and TOCSY studies 125
6.2.5 HM BC 127
6.3 Conclusions 128
References 129
Thesis Conclusions 131
B rief Bio-data o f the Author 134
