Study On Hetero-Phase Grafting Polymerization Of Vinyl Acetate (VAC), Maleic Anhydride (MAH) And VAC/MAH Binary Monomer System

This dissertation was designed to study hetero-phase grafting polymerization of vinyl acetate (VAC), maleic anhydride (MAH) and VAC/MAH binary monomer system, irrespectively, with low density polyethylene (LDPE) film as substrate and benzophenone (BP) as photoinitiator. The purpose is to develop new and more effective methods to modify the surface and buck properties of polyolefmes by studying the grafting mechanism of the system and exploring the characteristics of the grafting process.(1) To VAC/LDPE system, the main photografting principles and the effects of various factors were investigated in detail, and the grafting efficiency of different methods was assessed systematically. It was found that VAC can be smoothly photografted onto LDPE film with "film combination" system, e.g. conversion percent (CP) and grafting efficiency (GE) are 70% and 76%, irrespectively, with UV intensity of 5400w/cm2 and irradiation time of 3min. The reaction orders of polymerization rate to monomer concentration and photoinitiator concentration are about 1 and 0.76, irrespectively, showing that chain transfer reaction takes place with much ease in VAC/LDPE system.The photografting polymerization is affected greatly by oxygen mainly dissolved in monomer and photoinitiator solution, and it is not important whether or not the assembly unit is protected by nitrogen during UV irradiation. Increasing UV intensity and temperature appropriately facilitates the grafting polymerization; but the thicker of the reaction liquid, the more difficult for grafting polymerization to take place.The initiating efficiency of the two types of photoinitiators, i.e. Norrish I and Norrish II, was assessed, and it was shown that the former performs higher initiating polymerization reactivity, but the latter performs higher initiating grafting polymerization reactivity; inaddition, the typical Norrish type I photoinitiators possess ability to abstract hydrogen to some degree. Adding a bit of water to VAC/LDPE system is not only helpful to grafting polymerization, but to limiting it mostly within the surface layers of the LDPE film also. This disvovery certifies that water is beneficial to decrease chain transfer reaction in VAC system; and on the other hand, it is proved to be an effective way to limit grafting polymerization to surface regions of the substrate, which is very important to surface modification.Cross-linking reaction of this system was studied and it is clarified that photocross-linking reaction is inevitable to grafting polymerization. When Norrish type I photoinitiators are used, the grafting polymerization of VAC retards cross-linking reaction; but on the contrary, grafting polymerization of VAC accelerates cross-linking reaction by using Norrish type II photoinitiators.Several grafting methods designed were tested (e.g. simultaneous method, BP pre-absorbing method, and BP pre-coating method), and it is concluded that BP pre-coating method possesses a number of advantages such as introducing BP onto LDPE film quantitatively and easily.The absorption of BP and VAC by LDPE film is worth taking into consideration, because the distribution of BP and VAC on the substrate is a key factor to surface photografting polymerization. Their distribution can be adjusted with different solvents of BP and VAC. It is shown that only those solvents whoose solubility parameters (SP) are moderate or a bit low are applicable to restrict grafted chains mainly on LDPE film surface or within its sub-surface regions.(2) To MAH/LDPE system, due to the fact that little work has been done to study photografting polymerization of MAH in literature, so the process and characteristics of grafting MAH were investigated in detail, and three new grafting methods were developed, i.e. solution grafting method, melt grafting method and self-initiating grafting method. The main results are described below:1) When solution grafting method was utilized, MAH can be grafted onto LDPE film fair easily, e.g. CP and GE are 80% and 85%, irrespectively, with 3M MAH/ethyl acetate solution...