Metal alkyl borohydrides are used as initiators of polymerisation, particularly in adhesive compositions for bonding a wide range of substrates including low surface energy substrates such as polyolefins. As described, the metal alkyl borohydrides are of the formula I or II.
wherein
- R1 is C1-C10 alkyl,
- R2 and R3, which may be the same or different, are H, D, C1-C10 alkyl or C3-C10 cycloalkyl, phenyl, or phenyl-substituted C1-C10 alkyl or C3-C10 cycloalkyl, provided that any two of R1-R3 may optionally be part of a carbocyclic ring, and
- M+ is a metal ion.
In particular, alkali metal trialkyl borohydrides are used, the alkali metal salt being selected from: Lithium triethylborohydride, Sodium triethylborohydride, Potassium triethylborohydride, Lithium tri-sec-butylborohydride, Sodium tri-sec-butylborohydride, Potassium tri-sec-butylborohydride, and Lithium triethylborodeuteride. Other exemplified compounds which are less effective on low surface energy substrates include Lithium 9-borabicyclo [3.3.1]-nonane (9BBN) hydride, Lithium thexylborohydride, Lithium trisiamylborohydride and Potassium trisiamylborohydride.