Mechanism Research And Application Exploration On The Solid-state Photopolymerization Of Long-chain Vinyl Monomers

Compared with the traditional liquid-state photopolymerization,crystalline-state photopolymerization shows high polymerization rate and conversion,low volume shrinkage,and outstanding oxygen inhibition.Moreover,high crystallinity,high regio-and stereospecific polymer,even single crystal polymer,can be obtained through polymerization in crystalline state.However,the possibility of crystalline-state chain-reaction polymerization is disputable.For chain-reaction polymerization,a large number of double bonds need to move close to form the main chain of polymer.However,the long-chain vinyl monomers are close-packed in crystal,which restricts the deformation of molecule skeleton and the rotation of single bonds.The carbon-carbon double bonds of adjacent monomers can't move close enough to encounter,which cause that the crystalline-state polymerization of long-chain vinyl monomers is impossible.Nevertheless,researchers observed the crystalline-state polymerization of long-chain acrylate in experiment,which is inconsistent with expectation.Can crystalline-state chain-reaction polymerization occur?Does the observed polymerization in experiment really occur in crystal region?These problems are urgent to be answered.Herein,a modelization method to judge the possibility of photoinitiating free-radical chain-reaction polymerization in crystal region was established firstly.Based on this criteria,the crystalline states of octadecyl acrylate were found can't perform chain-reaction polymerization.Furthermore,the polymerization was proposed occur in rotator phases,which was confirmed by the method of molecular dynamics simulation.Then,binary systems of long-chain acrylates were constructed,which can enlarge the temperature range of rotator phases and stabilize the rotator phase.After that,through studing the phase behavior of long-chain vinyl ester,the relationship between the formation of rotator phase and the molecule structure was proposed.Finally,a porous crosslinked material was prepared ulitizing the feature that the conversion of rotator-state polymerization is controllable.This porous material showed good healing and shape memory properties,and the healing mechanism was discussed.The main work is showed as the following.1.A modelizaiton method to judge the possibility of free-radical chain propagation in crystal region was established,with which it could be inferred that the chain propagation can't occur in crystal region if the initial distances between atoms C2 of adjacent monomers are longer than 5.08 A.By using this method and the single crystal data of 1,6-hexanediol diacrylate,it is found that the 1,6-hexanediol diacrylate can't polymerize in crystal region,and the major contribution to conversion reported previously comes from the polymerization in amorphous region.2.Octadecyl acrylate was found exhibiting four solid phases:a-,sub-a-,?-and y-phase,which are hexagonal,orthorhombic,orthorhombic,and triclinic,respectively.The ?-phase is a set {?i},where i represent the content of defects.During the heating process,molecules in ?-phase will adjust the conformation to decrease the content of defects,which explained the reason of irreversible transition between the sub-?-phase and ?-phase.In addition,the?-phase can induce the newly generated ?-phase transforming into ?-phase directly during the cooling process,and two prerequisites of this induction process were proposed.3.The photopolymerization of octadecyl acrylate in four solid-state were studied,and it's found that although the ?-,sub-?-,and ?-phases of octadecyl acrylate are all satisfied the geometry criteria of chain-reaction polymerization in crystal,just a-and sub-?-phases showed high polymerization conversions.Based on these results,we firstly proposed and confirmed that the a-and sub-?-phases of octadecyl acrylate are rotator phases(R? and R? phases),and the ?-phase was orthorhombic crystal phase.The chain-reaction polymerization of octadecyl acrylate in rotator phase was confirmed by the method of molecular dynamics simulation.The flip of octadecyl acrylate,which is the distinguishing feature of rotator phases,enable two carbon-carbon double bonds of adjacent molecules move close enough for bonding.4.The binary systems of long-chain acrylates were constructed,which enlarged the temperature range of rotator phases and increased stability of the rotator phase.The binary systems exihibited higher conversion than each pure component,which showed obvious ultra-addition effect of‘0+0=2'.The mechanism of ultra-addition effect is that the conformation disorder at the end of molecules,due to the difference in chain length between two components,could restrict the shrinkage of lattice during the transition process from RI rotator phase to crystalline phase.It leads to the similar phase structures between crystalline phase and RI rotator phase,which finally stabilized the RI phase.Due to the RI phase(high reactivity)can transform back from the crystalline phase(low reactivity),the binary system showed ultra-addition effect of '0+0=2'.5.Four long-chain vinyl ester(V18,V16,V14 and V12)don't possess stable rotator phases,and it was found that the formation of rotator phases depends on the packing model of molecules.If the molecules have opportunities to pack untilted because of the electrostatic interaction of functional groups,the rotator phase may form with great potential.In addition,both the octadecyl acrylate(ODA)and vinyl stearate(V18)can induce the formation of rotator phase of vinyl palmitate(V16),but the induction effect of ODA was much better than that of V18.The end groups of ODA can bend in binary system and expand to the end of V16,which restrict the motion of V16 along its long axis,make the binary system of ODA-Y16 in untilted state,and finally induced the formation of rotator phase.However,the end group of V18 can just bend a little,which can't expand to the end of V16.Thus the induction effect of rotator phase in binary system of V18-V16 is relative weak.6.The porous material was obtained through the rotator-state photopolymerization of octadecyl acrylate followed by removing the residual monomers.The diameter of pores was about(5?20)?m.The porous poly(octadecyl acrylate)showed higher surface hydrophobicity,melting point,and swelling rate in n-hexane than that of non-porous poly(octadecyl acrylate).In addition,the porous in poly(octadecyl acrylate)gave the main chain and side chain of polymer enough spaces for moving,which endue the material with good self-healing and shape memory properties.