Crystallization Behaviors of Deuterated PCLs and Their Blends and Copolymers

Author:Li Wan

Supervisor:peng xiang fang


Degree Year:2019





Crystallization behaviors and structures of polymeric materials can significantly influence the end-use properties,such as thermal and mechanical properties,etc.,which makes the study on crystallization behaviors become one of the most advanced topics in the polymer field.In the past several decades,deuterium substitution has become an efficient technique to study the phase and crystallization behaviors of polymer blends or copolymers.However,current studies primarily focused on the application of deuterated polyolefins,investigation of other types of deuterated polymers,such as polyesters,are urgent needed.Besides,the deuterated polymer chains always exhibit different physical properties from hydrogenated chains and hence disturb the characterization signals.Even though intensive studies have focused on the deuterated polyethylene and got the basic knowledge of the properties variation from hydrogenated polymers to deuterated polymers,but recent researches on deuterated polypropylene,polyoxymethylene,and polythiophene found these newly synthesized deuterated species exhibit different variation of crystallization behaviors.For examples,partially selective deuterated polymers exhibt change varation of crystallization properties,but still lack systemtically investigation and mechanism study;The deuterated polymer systems with polar groups are still less understood;Several researchers have contrary views on the crystal structure of blends and copolymers,and still lack investigation under micro-and nano-length scale.Therefore,the dissertation synthesized typical semicrystalline deuterated poly(?-caprolactone)(PCL)as a model system to open the avenue of crystallization on deuterated polyesters,the crystallization of deuterated PCLs and their blends and copolymers were systematically investigated.Firstly,the dissertation synthesized deuterated PCLs.H-D exchange reactions were conducted to obtain the selectively deuterated cyclohexanone from cyclohexanone and fully deuterated cyclohexanone.Then,deuterated cyclohexanones were converted to deuteratedε-caprolactone monomers through oxidation process:fully protiated(d0),tetra deuterated at the3-and 7-ring positions(d4),hexa deuterated at the 4-,5-,and 6-ring positions(d6),and fully deuterated(d10).After that,four PCLs,D0,D4,D6,D10 were synthesized from the obtained?-caprolactones through ring-opening polymerization.Nuclear magnetic resonance and size exclusion chromatography were conducted to analyze the chemical structure of monomers and polymers.The non-isothermal and isothermal crystallization behaviors of selectively deuterated PCLs were investigated.In general,8),(8),and fitted08were found to decrease with the increase of deuterium.However,D4 and D6 showed different crystal growth manner after fiting to Avrami model,and also exhibit irregular relationship of8).Interactions between PCL chains were analyzed to explain the mechanism of8)(D6)>8)(D4).Besides London dispersion forces,additional weak hydrogen bonding interactions between the O atom(in the carbonyl group,C=O)and three nearby H atoms were found.The results provided useful information regarding isotope effects on selectively deuterated polymers,indicating the necessity of considering the crystallization properties when deploying fully or selectively deuterated labeling techniques.Then,the dissertation picked D0(H-PCL)and D10(D-PCL)samples to study the melt-phase behavior,Flory-Huggins interaction parametersχand the effect from chain-ends.Br terminated D-PCL blends,deuterated poly(ethylene oxide)(PEO)blends were synthesized as the control group.Small-angle neutron scattering(SANS)was used to analyze the melt-phase behaviors and the obtained curves were fitted by RPA and Zimm models.The results showed the characteristic of a homogeneous mixture of H and D chains with a temperature dependence negativeχvalues.H and D chains were miscible under testing temperature,theoretically,it would exhibt UCST behaviors.The effective negativeχin the H-and D-PCL blends is composited of“bare”polymer interaction and hydrogen bonding interaction,which is between the chain-end hydroxyl group and the carbonyl or ether group.Br terminated D-PCL blends exhibited nano-scale phase separation with the absence of hydroxyl group.The results showed perfect usage of RPA and Zimm model in the PCL melts,open the avenue forχmeasure between deuterated polymer chains with polar group.After that,the thermal behaviors,crystal structures and chain segments arrangement upon different crystallization conditions were investigated.High resolution powder diffraction found that D-PCL showed smaller lattice parameters than H-PCL in a,b(perpendicular to chain axis),and c(parallel to chain axis)directions.The contraction can be attributed to the reduction of inter-chain distance due to the smaller bond length of C-D than C-H,and the presence of attractive electrostatic interactions of ester groups in neighboring units in PCL.DSC results proved co-crystallization of some H and D chains.Polarized optical microscopy showed the micro-scale spherulites become larger with the increase of deuteration.Scattering results revealed the formation of separated H-and D-rich lamellaes with some degree of co-crystallization after slow cooling treatment.The long period obtained from SANS are twice of the long period from Small-angle X-ray scattering.Based on the theoretical analysis,H/D blends were found to form alternating H/D lamellar stacks.Besides,rapid cooling are proved that can prohibit the phase separation of H-and D-PCL contents effectively.Moreover,various triblock and random copolymers were synthesized.Melt-phase,segments arrangement of deuterated PCL copolymers upon different crystallization conditions and their relationship with SANS signals were investigated.The results showed that nano-scale phase separation and smaller homogeneous domains occurred simultaneously in the melt of D10-D0-D10.The parametersχin homogeneous were extracted and found one order smaller than theχin the blends.Influenced by the different cooling rate and tethering constraint between each segments,the symmetry D10-D0-D10 sample exhibt double SANS peaks and two different long periods with a two-fold relationship.Theoretical analysis proved that there were two contrast from the system,including the scattering length density(SLD)difference between lamellaes and amorphous and SLD difference between D10 rich lamellaes and the rest areas.The results systematically investigated the crystal structure model of H/D copolymers,built the relationship between crystal structure and small-angle scattering signals,thus enrich the fundament studies on deuterated polyesters,provide much-needed basic knowledge for the application of deuterium substitution.